This invention relates to syringes and more particularly to safety syringes of the kind comprising a telescopically moveable outer sleeve for covering a needle of the syringe, after use.
Various safety syringes of the kind referred to hereabove are known to the applicant. For example, in the specification of U.S. Pat. No. 4,655,751 to Harbaugh, there is disclosed such a safety syringe. The circular cylindrical sleeve of this syringe comprises a pair of integral, diametrically opposed and inwardly extending ears towards a rear end thereof. These ears, in use, co-operate with two pairs of opposed pockets defined respectively towards the rear and forward ends of a tube or barrel of the syringe. To release the ears from the rearward pockets, it is necessary to exert a force in a radially inwardly direction on the sleeve thereby to deform, more particularly, to oval the shape of the sleeve. This force must be exerted in opposed regions of the sleeve, spaced substantially ninety degrees from the ears. Finger grips are also provided on the sleeve in these regions.
The disadvantages of this syringe are that it is as easy to deform the sleeve and to release the ears from the pair of forward pockets and thereby to remove the sleeve from the tube, as it is to release the ears from the aforementioned rearward pockets. Thus, the sleeve is releasably locked in both its first and second positions. Furthermore, the ears and finger grips which are disposed at ninety degree intervals on the sleeve obscure the visibility of graduation marks on the tube of the syringe. Still furthermore, the pockets and channels defined in the outer surface of the tube require too drastic a departure from the know and conventional design of tubes or barrels for syringes.